Devilfish kit does not come with the bits for a
SMS , those are in the hammerhead/skyray kit, on the heavy weapon sprue.
I have made a lot of
sms for my devilfish and I use some plastic card and make small rectangular boxes, aprox the size of the misslepod/
sms, and them mount them using the drone upperhull and its circular base stand bit ( the one that you attach the pulse carbines to.
in the pic below I have done that on the two hammerheads on each side of the ethereal.
Plastic card is easy to find at most hobby shops, and model railroad stores.
or from this site.
http://www.evergreenscalemodels.com/Sheets.htm#Square Tile
I use item no. 4503, it comes with a 1/8" tile pattern that makes accurate sizing easy.
hope this helps,